Can you tell me is propelyn glycol (e-cigs) harmful to the lungs?

Wish I could: While there does not appear to be any obvious toxicity, it simply has not been studied, because courts have ruled that the fda does not have jurisdiction over it, and the manufacturers have not been required to do any safety or other studies. So, nobody really knows - not only the effects of the propylene glycol, but of the other additives, flavors and preservatives that may be present.